Ion beam-assisted methods for depositing DLC coatings are well known. Typically, such methods take place in a vacuum and involve first volatilizing a fluid hydrocarbon precursor, such as polyphenyl ether, and then condensing the volatilized precursor onto the surface of a workpiece while simultaneously subjecting the surface to energetic ion bombardment. The ion bombardment ruptures the carbon-hydrogen bonds in the precursor film, allowing the hydrogen to be pumped away, leaving the workpiece coated with a hard residual DLC coating.
Unfortunately, when a fluid precursor is heated in a vacuum, the fluid precursor sometimes spatters, causing droplets of precursor material to form on the surface of the workpiece. These droplets can prevent the energetic ion beam from adequately penetrating the precursor material, thereby preventing full conversion of the precursor droplet into DLC. Also, many fluid precursors tend to absorb water vapor if they are exposed to the atmosphere. Upon vaporization of the precursor, the absorbed water vapor is released as steam. The release of steam can lead to irregular vaporization of the precursor and can create droplets on the workpiece due to the sudden local release of water vapor from the precursor material. The result can be an unacceptable coating, the most common problem being the presence of pinholes which can cause erosion of the DLC coating and, eventually, corrosion of the substrate.
One way to overcome the foregoing problems might be to use a different type of precursor for the DLC coating. Any DLC precursor should have a low vapor pressure so that the precursor will condense to form a film that will not volatilize before it is converted to DLC. Preferably, the precursor material can be vaporized at a relatively low temperature. Also, the precursor preferably should not deleteriously decompose during vaporization.
Several materials besides polyphenyl ether have been used as precursors for ion-assisted deposition of DLC. Unfortunately, the current alternates to polyphenyl ether, such as poly dimethyl siloxane, are liquid and therefore have the same problem of droplet formation and water absorption as polyphenyl ether. A DLC precursor that does not present these problems would be highly desirable.